Such droplet dispensing devices are also sometimes called aerosol generators, nebulizers and the like. They normally contain a nozzle body on a support part, in particular, a nozzle body of a liquid droplet spray device which dispenses a liquid substance as a liquid droplet spray or from the device through the nozzles of the nozzle body. They further consist of an actuator based on a vibrating element which generally causes the liquid to vibrate, to be accelerated and expelled as droplets. They further consist of elements such as liquid space, liquid feed and fluid interface to a reservoir, a reservoir as well as electrical connections between the vibrating element and a corresponding electronic circuitry. The elements may be contained in the aforementioned support part, in a further support part or they may be contained in a number of support parts. The support part or parts and elements need to be manufactured and assembled with the actuator and the vibrating element. The liquid may be for example an ambient fragrance, a perfume, an insecticide, a liquid pharmaceutical formulation, aqueous based liquids and flammable or combustible liquids.
Such nozzle bodies are sometimes called aperture plates, nozzle arrays, dosing aperture, orifice plate, vibratable membrane member, dosing aperture arrangement, aerosol generator and the like. The terms are hence to be understood as being interchangeable throughout the present document.
In fact, such nozzle bodies and droplet spray devices are well known. For example see the document EP 1 129 741 in the name of the present Applicant. This document describes a liquid droplet spray device having a top substrate formed of a main body and of a nozzle body. The nozzle body contains a nozzle array of liquid droplet outlet means allowing a liquid substance contained in the liquid droplet spray device to exit the device, in this case as a spray of droplets. The nozzle body is conventionally formed of a nozzle array made out of silicon, a polymer, a resin such as SU-8, Nickel, a metal alloy, Parylen, Duroplast or any suitable material or combination of these and other materials that allows for a sufficiently precise and cost-effective manufacturing of the outlet nozzle array. Beyond well-known silicon, metal and SU-8 resin micro-machining methods the nozzle array could also be produced by methods using tools made with silicon micro-machining and other known replication methods like LIGA (Lithography-Galvano forming), hot embossing, UV printing, polymer and powder micro-injection moulding, micro-EDM and similar advanced 3D micro-machining methods and suitable combination of methods using photolithography and micro-structuring of resins, silicon, metal and plastic.
The documents U.S. Pat. No. 6,722,582 and EP 1 273 355 also in the name of the present applicant disclose such micro-machining methods.
The document PCT/EP2006/006059, in the name of the present Applicant, shows a droplet spray device including the nozzle body, the support parts and the actuator containing the vibrating element as well as a general way of assembling such a device.
Documents US 2004/0263567 and EP-A-1 604 701 also in the name of the present Applicant, show examples of various device configurations for which such a droplet spray device can be produced and needs to be assembled into in an efficient and cost-effective manner.
Another device is known from the document U.S. Pat. No. 4,702,418 which describes a piezoelectric aerosol dispenser that has eccentric liquid inlet/outlet means, and a nozzle chamber having a nozzle region proximate a single nozzle and a larger reservoir interconnected to the nozzle region. The nozzle region is gravity fed through a restrictive channel. Further, a piezoelectric bender is used to drive fluid from the reservoir region to the nozzle region and from the nozzle region through the single nozzle to create an aerosol spray. Such an arrangement with a piezoelectric bender does not allow for a controlled release of fluid, as the fluid must first be pumped from the reservoir region and then expelled from the nozzles without interference of one flow with the other. Further, precise control while using a piezoelectric bender is virtually impossible.
As can be seen from the cited prior art documents, all of them approach mainly a particular aspect of the manufacturing of a particular component of the respective droplet spray devices, but fail to take a total device approach to the industrial production and assembly of components and device. In fact these devices, together with others fall into the category of Multi-Material-Electro-Mechanical Systems. Generally, the construction, the production and the assembly of such devices requires to dominate several main criteria or problems which additionally to attaining the lowest possible cost may present contradictory effects and conditions.
The effects and conditions firstly refer to the need to provide capillary feed or feed at very low pressures well below one mbar (100 Pa) or fractions thereof. Capillary feed for some liquids will refer to liquid channel, chamber and other fluid handling structures or features with dimensions of a few hundred microns to below 100 μm, often in the range of 10 to 50 μm, absolute evenness and smoothness of wetted surfaces and absence of dead spaces, corners and pockets in order to avoid even minute bubble traps. These bubbles, consisting of air surrounded by an ultra-thin film of the liquid, tend to block the capillary feed, hence the device functionality in a very effective manner.
The second problem is to assemble the actuator in a way which provides the most efficient use of the ultrasonic energy delivered by the vibrating element, namely a piezoelectric element.
The third problem is that leak-tightness needs to be guaranteed for a variety of liquids. Leak-tightness normally implies rigid body construction and assembly of its components and long-term resistance of the components to sometimes aggressive solvents.
A further problem is the aforementioned lowest possible production cost together with a minimum of assembly operations in simple, reliable assembly steps.
A further problem is represented by the need to disassemble the droplet spray device after one or several uses in order not to discard all parts after use, but to discard only one part and to keep the others for further use after cleaning for example or to disassemble some parts for cleaning them periodically and to reassemble them again for further use.
As can be understood by the person skilled in the art, these criteria can be highly contradictory in their requirements and effects. Also, as said before, none of the prior art devices discloses on how to achieve these contradictory criteria in one device or a family of devices.
Other prior art devices have addressed in more detail some individual problem areas. For example, document U.S. Pat. No. 6,926,208 discloses a fluid injection device with an aperture plate having an oscillating surface with tapered apertures thereon and various relatively complex combinations of fluid supply to the oscillating surface. Again this document is in general silent about how this feature can be integrated into a final device providing leak-tightness, fluidic optimization and low cost integration.
In view of the above problems, the present Applicant has filed a co-pending application EP 07 002 190.2 relating to a dispensing device that overcomes the abovementioned problems.
This document EP 07 002 190.2 describes a volatile liquid dispenser device for ejecting liquid as a spray of droplets. A piezoelectric element acts on the liquid so as to cause the liquid to undergo vibration by transmission of the ultrasound from the piezoelectric element to the liquid. This device is schematically shown in FIG. 1, which shows a detailed view of a cross-section cut of the dispensing device, which comprises a first substrate 1 and a second substrate 3. An actuating membrane 2 is positioned between first substrate 1 and second substrate 3, and can be actuated, i.e. put into vibration, by way of a vibrating element 6 suitably attached thereto.
First substrate 1 is provided with a space 5, for example a recessed portion, allowing to receive liquid that is to be expelled through ultrasound transmission from the vibrating element 6 to the liquid. This space 5, once filled with liquid, thus constitutes a pressure chamber for ejecting the liquid contained therein. First substrate 1 further comprises liquid droplet outlet means 4 suitably arranged to allow for ejection of the liquid there through. This liquid droplet outlet means 4 generally is a spray head consisting of a perforated membrane having a nozzle array, in a manner well known in the art.
However, the Applicant has found that this device only partially addresses the above-mentioned problem relating to efficiency of ultrasonic sound transmission so as to allow for improved efficiency of a piezoelectric element for actuating the liquid to be expelled. It seems that some transmission efficiency is lost from vibrating element 6 to actuating element 6 and then to liquid in space 5.
If this ultrasonic sound transmission can be further improved, a reduction in power consumption can be achieved, which is important especially when using battery-powered devices.
Also, this device has a further problem in that space 5 of the first substrate for containing liquid is formed as a recessed opening in the first substrate. This means that the first substrate cannot be dissociated from second substrate 3 when liquid is present in space 5, as the liquid will spill out. This leads to undesirable assembly constraints.
It is, therefore, an object of the present invention to provide an innovative droplet spray device that overcomes the inconveniences presented by the prior art documents.
Thus, the present invention concerns the construction of an innovative dispenser device fulfilling these objectives efficiently and in various embodiments which may be obtained in a relatively simple and inexpensive manner.